Multilayer thermoformable structure

ABSTRACT

This invention relates to a multilayer thermoformable structure comprising (A) at least one cap layer and (B) at least one core layer, and polymer compositions for making the same. The multilayer structures and polymer compositions of the invention are useful in preparing thermoformed articles and are particularly useful in preparing liners for refrigerators and freezers. The multilayer structures and the polymer composition have good thermoformability and chemical resistance. The multilayer structures and the polymer composition have good surface properties including a glossy finish. Further these materials are compatible with new blowing agents, such as the hydrochlorofluorocarbons and hydrofluorocarbon blowing agents, which are more environmentally friendly. The layers of the multilayer structure do not require a glue layer.

This is a continuation-in-part of copending application(s) Ser. No.07/948,080 filed on Sep. 21, 1992, now U.S. Pat. No. 5,264,280.

TECHNICAL FIELD OF THE INVENTION

This invention relates to multilayer structures, such as laminants, andpolymer composition for making the same.

BACKGROUND OF THE INVENTION

The multilayer structures and the blended polymer compositions of thisinvention may be used in a variety of applications includingrefrigeration parts, such as inner liners, inner door panels, innertrim, trays and shelves, etc. The multilayered structures and theblended polymers are useful in preparing parts for: the automotiveindustry; communications such as telephones, radio, TV, cassettes, etc.;power tools; appliances; business machines; toys; furniture; etc. Themultilayered structure and polymers must provide a good quality surfacewhich has a glossy finish and is resistant to chemicals and scuffing.

When preparing multilayer structures, the layers of the structures mustadhere to each other. If the layers of the structure do not adhere toeach other a glue, or tie layer is used to stick the layers of thestructure together. Layers which adhere to each other without a gluelayer are useful.

The concerns about the environmental affects of chlorofluorocarbons(CFCs) on the earth's ozone layer have led to the development of blowingor foaming agents for foams, such as polyurethane foams used asinsulation. The new blowing agents contain little or no chlorine. Oneproblem associated with the new blowing agents is their chemical attackon the linings of refrigerators and freezers. A stable and chemicallyresistant lining material for refrigerators and freezers is needed.

SUMMARY OF THE INVENTION

This invention relates to a multilayer thermoformable structurecomprising

(A) at least one cap layer of a polymer composition comprising (i) atleast about 50% to about 80% by weight of a high impact polystyrene,(ii) from about 0% to about 45% by weight of at least one block polymerof a vinyl aromatic monomer and an aliphatic conjugated diene, aselectively hydrogenated derivative thereof, or a selectivelyhydrogenated derivative thereof to which has been grafted a unsaturatedcarboxylic reagent, wherein the block polymer contains up to about 50%by weight bound styrene, and (iii) from about 0% to about 45% by weightof at least one block polymer of a vinyl aromatic monomer and aconjugated diene, a partially hydrogenated derivative thereof, or aselectively hydrogenated derivative thereof to which has been grafted aunsaturated carboxylic reagent, wherein the block polymer containsgreater than about 60% by weight bound vinyl aromatic monomer, with theproviso that the cap layer includes at least one of (Aii) or (Aiii); and

(B) at least one core layer selected from the group consisting of

(1) at least one polymer composition comprising (i) from about 50% toabout 80% by weight of at least one polyolefin, (ii) from about 10% toabout 30% by weight of a polymer of a vinyl aromatic compound and anunsaturated dicarboxylic acid anhydride or imide, or mixtures thereof;and (iii) from about 5% to about 20% by weight of a block polymer of avinyl aromatic compound and a conjugated diene, a partially hydrogenatedderivative thereof, or a selectively hydrogenated derivative thereof towhich has been grafted a unsaturated carboxylic reagent;

(2) at least one polymer composition comprising (i) from about 50% toabout 80% by weight of a polyolefin, (ii) from about 10% to about 30% byweight of a homopolymer of a vinyl aromatic monomer, or a polymer of avinyl aromatic monomer and at least one monomer selected from the groupconsisting of acrylic acid or ester, methacrylic acid or ester,acrylonitrile and maleic anhydride; (iii) from about 5% to about 20% byweight of at least one block polymer of a vinyl aromatic monomer and analiphatic conjugated diene, a partially hydrogenated derivative thereof,or a selectively hydrogenated derivative thereof to which has beengrafted a unsaturated carboxylic reagent;

(3) at least one polymer composition comprising (i) from about 70% byweight of at least one polyolefin, (ii) from about 5% to about 30% byweight of a block polymer of a vinyl aromatic compound and a conjugateddiene, a partially hydrogenated derivative thereof, or a selectivelyhydrogenated derivative thereof to which has been grafted a unsaturatedcarboxylic reagent, wherein the block polymer is derived from at leastabout 60% by weight bound vinyl aromatic monomer; and (iii) from about0.3% to about 15% by weight of a block polymer of a vinyl aromaticcompound and a conjugated diene, a partially hydrogenated derivativethereof, or a selectively hydrogenated derivative thereof to which hasbeen grafted a unsaturated carboxylic reagent, wherein the polymer isderived from up to about 50% by weight bound vinyl aromatic monomer.

The invention also relates to a polymer composition useful in makingmultilayered structures. The polymer composition includes a polymercomposition comprising (i) at least about 50% to about 80% by weight ofa high impact polystyrene, (ii) from about 1% to about 45% by weight ofat least one block polymer of a vinyl aromatic monomer and an aliphaticconjugated diene, a selectively hydrogenated derivative thereof, or aselectively hydrogenated derivative thereof to which has been grafted aunsaturated carboxylic reagent, wherein the block polymer contains up toabout 50% by weight bound styrene, and (iii) from about 0.3% to about45% by weight of at least one block polymer of a vinyl aromatic monomerand a conjugated diene, a partially hydrogenated derivative thereof, ora selectively hydrogenated derivative thereof to which has been grafteda unsaturated carboxylic reagent, wherein the block polymer containsgreater than about 60% by weight bound vinyl aromatic monomer.

The multilayer structures and polymer composition of the invention areuseful in preparing thermoformed articles and are particularly useful inpreparing liners for refrigerators and freezers. The multilayerstructures and the polymer composition have good thermoformability andchemical resistance. The multilayer structures and the polymercomposition have good surface properties including a glossy finish.Further these materials are compatible with new blowing agents, such asthe hydrochlorofluorocarbon and hydrofluorocarbon blowing agents. Thesematerials are more environmentally friendly. The layers of themultilayer structure do not require a glue layer and are generallyrecyclable.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Unless the context indicates otherwise, throughout the specification andclaims, the amount of the polymers present is determined exclusive offiller or other nonpolymer additive in the polymer compositions.Therefore the amount of each polymer is determined by dividing theweight of the polymer by the combined weight of all polymers present inthe composition.

Cap Layer (A)

The multilayer structure has a cap layer (A). This cap layer comprises apolymer composition comprising a polymer composition comprising (i) atleast about 55% by weight of a homopolymer of a vinyl aromatic monomer,or a polymer of a vinyl aromatic monomer and at least one monomerselected from the group consisting of a mono- or dicarboxylic reagentand other vinyl monomers, (ii) from about 0% to about 45% by weight ofat least one block polymer of a vinyl aromatic monomer and an aliphaticconjugated diene, a selectively hydrogenated derivative thereof, or aselectively hydrogenated derivative thereof to which has been grafted aunsaturated carboxylic reagent, wherein the block polymer contains up toabout 50% by weight bound styrene, and (iii) from about 0% to about 45%by weight of at least one block polymer of a vinyl aromatic monomer anda conjugated diene, a partially hydrogenated derivative thereof, or aselectively hydrogenated derivative thereof to which has been grafted aunsaturated carboxylic reagent, wherein the block polymer containsgreater than about 60% by weight bound vinyl aromatic monomer, with theproviso that the cap layer includes at least one of (Aii) or (Aiii). Inone embodiment, the polymer (Ai) is a high impact polystyrene.

In one embodiment, the cap layer is prepared from polymer compositionswhich are free of polyamides, e.g. nylon polymers. In anotherembodiment, the cap layer polymer compositions are free of polyurethane.In another embodiment, the cap layer polymer compositions are free ofpolyphenylene ether resins. In another embodiment, the cap layer iscontains less than 30%, or about 20%, or about 10% by weight polyolefin,such as polymers of ethylene and polypropylene. In another embodiment,the cap layer is free of polyolefin.

Polymers of Vinyl Aromatic Monomers (Ai)

The multilayer structures may include a homopolymer of a vinyl aromaticmonomer, or a polymer of a vinyl aromatic monomer and at least onemonomer selected from the group consisting of acrylic acid or ester,methacrylic acid or ester, acrylonitrile and maleic anhydride. (Ai) isgenerally present in an amount from about 50%, or about 55%, or about60% up to about 85%, or to about 80%, or to about 75%, or to about 72%by weight.

The vinyl aromatic monomer includes styrene and the various substitutedstyrenes. In one embodiment, the vinyl aromatic monomer is representedby the following formula ##STR1## wherein R is hydrogen, an alkyl groupcontaining from 1 to about 6 carbon atoms, or halogen; Z is a memberselected from the group consisting of vinyl, halogen and alkyl groupscontaining from 1 to about 6 carbon atoms; and p is a whole number from0 up to the number of replaceable hydrogen atoms on the phenyl nucleus.Specific examples of vinyl aromatic compounds such as represented by theabove formula include, for example, in addition to styrene,alpha-methylstyrene, beta-methylstyrene, vinyl toluene, 3-methylstyrene,4-methylstyrene, 4-isopropylstyrene, 2,4-dimethylstyrene,o-chlorostyrene, p-chlorostyrene, o-bromostyrene,2-chloro-4-methylstyrene, etc. Styrene is the preferred vinyl aromaticcompound.

Specific examples of polymers of vinyl aromatic compounds includepolystyrene, poly(alpha-methylstyrene), poly(p-methylstyrene) and highimpact polystyrene (HIPS). Polystyrene is a preferred vinyl aromatichomopolymer. A commercially available polystyrene, which is useful inthis invention is Dart 108 polystyrene from Dart Polymer Inc.

In one embodiment, the polymer (A1i) is a high impact polystyrene. Ahigh impact polystyrene is a polystyrene resin which contains an impactmodifier. Impact modifiers are known and include rubber or elastomericcompounds. The impact modifiers include homopolymers or copolymers ofbutadiene, isoprene, and ethylene-propylene diene toohomers.

High impact polystyrenes are known and available commercially fromAmoco, Chevron, Dow, and Polysar. Useful high impact polystyrenesinclude Mobil 7863 and 5600, available commercially from MobilCorporation; Polystyrene HT-54, available from Idemitsu PetrochemicalCo.; and Amoco H2R, available commercially from Amoco Chemical Company.The preferred range for the high impact polystyrene is from about 50% upto about 80% by weight of the polymer composition. The inventors havefound that below 50% by weight of high impact polystyrene the polymercomposition is not a continuous phase. Amounts of high impactpolystyrene above 80% by weight lead to loss of adhesion between the capand core layers and/or loss of flexibility of the cap layer.

In another embodiment, (Ai) is a polymer of a vinyl aromatic monomer anda monomer selected from the group consisting of an unsaturated mono- ordicarboxylic reagent and other vinyl monomers. The carboxylic reagentsinclude carboxylic acids per se and their functional derivatives such asanhydrides, imides, metal salts, esters, etc., which are capable ofbeing forming polymers with the vinyl aromatic monomer.

The unsaturated monocarboxylic acid reagents are carboxylic acids andesters corresponding to the formula

    RCH=C(R.sub.1)COOR.sub.2

wherein R is hydrogen or a saturated aliphatic or alicyclic, aryl,alkaryl or heterocyclic group; R₁ is hydrogen or an alkyl group; and R₂is hydrogen or an alkyl, aryl, or heterocyclic group. Preferably, R ishydrogen or an alkyl group containing from 1 to about 10 carbon atoms.Preferably, R₁ is hydrogen or an alkyl group containing from 1 to about10 carbon atoms. Preferably, R2 is hydrogen or an alkyl group havingfrom 1 to about 10 carbon atoms. The total number of carbon atoms in R₁and R2 should not exceed 18 carbon atoms. Specific examples of usefulmonobasic carboxylic reagents include acrylic acid, methacrylic acid,crotonic acid, acrylic anhydride, etc. Specific examples of estersinclude methyl, ethyl, propyl, and butyl acrylate and methacrylate.

In another embodiment, the unsaturated carboxylic reagent is adicarboxylic reagent. An example of dicarboxylic reagents are maleicreagents. The maleic reagents may generally be represented by theformula ##STR2## wherein each R group is hydrogen or an aliphatic oraromatic hydrocarbyl group or the two R groups are joined together toform a fused ring derivative, X is -O- or >NR₂ where R2 is hydrogen or ahydrocarbyl group which may be an aliphatic or an aromatic hydrocarbylgroup such as phenyl, methyl, ethyl, propyl, butyl, etc. Preferably bothR groups are hydrogen.

Examples of maleic derivatives which are cyclic or bicyclic compoundsinclude those obtained by a Dieis-Alder reaction of butadiene withmaleic anhydride or a maleimide. Those obtained by a Dieis-Alderreaction of cyclopentadiene with maleic anhydride or maleimide, andthose obtained by a Dieis-Alder reaction of isoprene with maleicanhydride or an N-substituted maleimide. These cyclic or bicyclicderivatives have high glass transition temperatures. Examples ofdicarboxylic reagents include maleic acid, maleic anhydride, fumaricacid, mesaconic acid, itaconic acid, citraconic acid, itaconicanhydride, citraconic anhydride, monomethyl maleate, monosodium maleate,etc.

The copolymers of the vinyl aromatic monomers with maleic anhydride,N-substituted maleimides or metal salts of maleic acid are obtained, inone embodiment, by polymerizing equimolar amounts of styrene and theco-reactant, with or without one or more interpolymerizable comonomers.In another embodiment, substantially homogeneous copolymers of styrenewith maleic arthydride or maleimide or metal salts of maleic acid can beobtained by (1) heating o a vinyl aromatic monomer to a temperature atwhich the vinyl aromatic monomer will polymerize, (2) stirring thepolymerizing vinyl aromatic monomer while (3) adding maleic anhydride,maleimide, or the metal salt of maleic acid, or mixtures thereof at acontinuous and uniform rate. Generally, the addition of the maleicanhydride, maleimide, or metal salts or esters of maleic acid is made ata rate in moles per unit time that is slower than the rate, in moles perunit time at which the vinyl aromatic monomer is polymerizing.Procedures for preparing such copolymers are known in the art and havebeen described in, for example, U.S. Pat. No. 2,971,939.

In one embodiment, (Ai) is a styrene-maleic anhydride copolymer. Thestyrene-maleic anhydride copolymers (SMA) are available commerciallyfrom, for example, ARCO under the general trade designation Dylark.Examples include: Dylark DBK-290 reported to comprise about 18% byweight of maleic anhydride and about 82% by weight of styrene; Dylark332 reported to comprise about 14% by weight of maleic anhydride and 86%by weight of styrene; and Dylark 134 reported to comprise about 17% byweight of maleic anhydride, the balance being styrene.

Other Dylark materials available include transparent grades: Dylark 132(Vicat 109° C), Dylark 232 (Vicat 123° C.) , and Dylark 332 (Vicat 130°C.). Impact grades include Dylarks 150, 250, 350 and 700 which arebelieved to be blends and/or grafts of SMA with SBR.

Other examples of impact modified styrenic and alpha-methyl styrenecopolymers with maleic arthydride and acrylonitrile include Arvyl 300 MRand 300 CR.

Low molecular weight styrene-maleic anhydride copolymers (Mw as low as1500) also are useful and these are available commercially such as fromMonsanto under the designation "Scripset" and from Atochem under thedesignation "SMA Resins". Sulfonated styrene-maleic arthydridecopolymers (and their metal salts) also are available and useful in thisinvention. Two such products are available from Atochem: SSMA-1000 whichis a sulfonated copolymer of about 50% styrene and 50% maleic anhydride;and SSMA 3000, a sulfonated SMA comprising about 75% styrene and 25%maleic anhydride.

Specific examples of copolymers of vinyl aromatic compounds include:styreneacrylonitrile (SAN); styrerie-acrylic acid; and styrenemethacrylic acid.

Block Polymers (Aii)

The multilayered structure also includes a block polymer of a vinylaromatic monomer and a conjugated diene, a partially hydrogenatedderivative thereof, or a selectively hydrogenated derivative thereof towhich has been grafted a unsaturated carboxylic reagent. The blockpolymer of a vinyl aromatic monomer and an aliphatic conjugated diene(Aii) is typically present in an amount from about 10%, or about 15% upto about 30%, or to about 25% by weight of the polymer composition. Theblock polymer (Aii) contains up to about 50% bound vinyl aromaticmonomer. In one embodiment, (Aii) contains up to about 48%, or to about45% bound vinyl aromatic monomer.

The block polymers, usually block copolymers, may be diblock, triblock,multiblock, starblock, polyblock or graftblock polymers. Throughout thisspecification and claims the terms diblock, triblock, multiblock,polyblock, and graft or grafted-block with respect to the structuralfeatures of block polymers are to be given their normal meaning asdefined in the literature such as in the Encyclopedia of Polymer Scienceand Engineering, Vol. 2, (1985) John Wiley & Sons, Inc., New York, pp.325-326, and by J.E. McGrath in Block Copolymers, Science Technology,Dale J. Meier, Ed., Harwood Academic Publishers, 1979, at pages 1-5.

Such block polymers may contain various ratios of conjugated dienes tovinyl aromatic monomer. Accordingly, multi-block polymers may beutilized which are linear or radial symmetric or asymmetric and whichhave structures represented by the formulae A-B, A-B-A, A-B-A-B, B-A-B,(AB)₀,1,2 BA, etc., wherein A is a polymer block of a vinyl aromaticmonomer or a conjugated diene/vinyl aromatic monomer tapered polymerblock, and B is a polymer block of a conjugated diene.

The block polymers may be prepared by any of the well-known blockpolymerization or copolymerization procedures including sequentialaddition of monomer, incremental addition of monomer, or couplingtechniques as illustrated in, for example, U.S. Pat. Nos. 3,251,905;3,390,207; 3,598,887; and 4,219,627. As well known, tapered polymerblocks can be incorporated in the multi-block copolymers bycopolymerizing a mixture of conjugated diene and vinyl aromatic monomermonomers utilizing the difference in their copolymerization reactivityrates. Various patents describe the preparation of multi-blockcopolymers containing tapered copolymer blocks including U.S. Pat. Nos.3,251,905; 3,639,521; and 4,208,356, the disclosures of which are herebyincorporated by reference.

Conjugated dienes which may be utilized to prepare the polymers andcopolymers are those containing from 4 to about 10 carbon atoms and moregenerally, from 4 to 6 carbon atoms. Examples include from1,3-butadiene, 2-methyl- 1,3-butadiene (isoprene),2,3-dimethyl-l,3-butadiene, chloroprene, 1,3-pentadiene, 1,3-hexadiene,etc. Mixtures of these conjugated dienes also may be used. The preferredconjugated dienes are isoprene and 1,3-butadiene.

The vinyl aromatic monomers which may be utilized to prepare thecopolymers are described above. The preferred vinyl aromatic monomer isstyrene.

Many of the above-described polymers of conjugated dienes and vinylaromatic compounds are commercially available. The number averagemolecular weight of the block polymers, prior to hydrogenation, is fromabout 20,000 to about 500,000, preferably from about 40,000 to about300,000.

The average molecular weights of the individual blocks within thepolymers may vary within certain limits. In most instances, the vinylaromatic block will have a number average molecular weight in the orderof about 2000 to about 125,000, and preferably between about 4000 and60,000. The conjugated diene blocks either before or after hydrogenationwill have number average molecular weights in the order of about 10,000to about 450,000 and more preferably from about 35,000 to 150,000.

Also, prior to hydrogenation, the vinyl content of the block polymer isfrom about 10 to about 80%, and the vinyl content is preferably fromabout 25 to about 65%, particularly 35 to 55% when it is desired thatthe modified block polymer exhibit rubbery elasticity. The vinyl contentof the block polymer can be measured by means of nuclear magneticresonance.

Specific examples of diblock polymers include styrene-butadiene,styrene-isoprene, and the hydrogenated derivatives thereof. Examples oftriblock polymers include styrene-butadiene-styrene,styrene-isoprene-styrene,alpha-methylstyrene-butadiene-alpha-methylstyrene, alpha-methylstyrene-isoprene-alpha-methylstyrene, and their partially hydrogenatedderivatives. The diblock and triblock polymers are commerciallyavailable from a variety of sources under various tradenames. An exampleof a commercially available diblock resin includes Solprene 314D(Phillips). A number of styrene-butadiene-styrene triblock polymers aresold by the Shell Chemical Company under the trademarks "Kraton 2103","Kraton 2104", and "Kraton 2113". Such thermoplastic rubbery blockpolymers are made by anionic polymerization, and the above threeidentified Shell Kratons differ in molecular weight and viscosity, andalso in the ratio of butadiene to styrene. For example, "Kraton 2103"and "Kraton 2113" have a styrene to butadiene ratio of 28:72 while"Kraton 2104" as a styrene to butadiene ratio of 30: 70. Blends ofdiblock and triblock polymers are also available. Kraton 1118 (Shell) isa blend of SB diblock and SBS triblock polymers. A particularly usefulstyrenebutadiene block copolymer is Kraton G1701X.

Multiblock polymers of styrene and either isoprene or butadiene also arecommercially available. Commercially available and preferredstyrene-butadiene multiblock polymers include Stereon 841A (43%styrene:57% butadiene) and Stereon 845A which are available from TheFirestone Tire & Rubber Company.

Radial or starblock copolymers are available from Fina under the generaldesignation "Finaprene SBS Polymer". A particularly useful radial orstarblock polymer is available commercially under the designation"Finaprene 414".

The selective hydrogenation of the block polymers may be carried out bya variety of well known processes including hydrogenation in thepresence of such catalysts as Raney nickel, noble metals such asplatinum, palladium, etc., and soluble transition metal catalysts.Suitable hydrogenation processes which can be used are those wherein thediene-containing polymer or polymer is dissolved in an inert hydrocarbondiluent such as cyclohexane and hydrogenated by reaction with hydrogenin the presence of a soluble hydrogenation catalyst. Such procedures aredescribed in U.S. Pat. Nos. 3,113,986 and 4,226,952, the disclosures ofwhich are incorporated herein by reference. Such hydrogenation of theblock polymers which are carried out in a manner and to extent as toproduce selectively hydrogenated polymers having a residual unsaturationcontent in the polydiene block from about 0.5 to about 20% of theiroriginal unsaturation content prior to hydrogenation.

In one embodiment, the conjugated diene portion of the block polymer isat least 90% saturated and more often at least 95% saturated while thevinyl aromatic portion is not significantly hydrogenated. Particularlyuseful hydrogenated block polymers are the hydrogenated block polymersof styrene-isoprene-styrene such as an (ethyloene/propylene)-styreneblock polymer. When a polystyrene-polybutadiene ratio in polymer ishydrogenated, it is desirable that the 1,2-polybutadiene to1,4-polybutadiene ratio in the polymer is from about 30:70 to about70:30. When such a block polymer is hydrogenated, the resulting productresembles a regular polymer block of ethylene and 1-butene (EB). Asnoted above, when the conjugated diene employed as isoprene, theresulting hydrogenated product resembles a regular polymer block ofethylene and propylene (EP). One example of a commercially availableselectively hydrogenated is Kraton G-1652 which is a hydrogenated SBStriblock comprising 30% styrene end blocks and a midblock equivalent isa polymer of ethylene and 1-butene (EB). This hydrogenated block polymeris often referred to as SEBS.

In another embodiment, the selectively hydrogenated block polymer is ofthe formula

    B.sub.n (AB).sub.o A.sub.p

wherein n=0 or 1;

o is 1 to 100;

p is 0 or 1;

each B prior to hydrogenation is predominantly a polymerized conjugateddiene hydrocarbon block having a number average molecular weight ofabout 20,000 to about 450,000;

each A is predominantly a polymerized vinyl aromatic monomer blockhaving a number average molecular weight of from about 2000 to about115,000; the blocks of A constituting about 5% to about 95% by weight ofthe polymer; and the unsaturation of the block B is less than about 10%of the original unsaturation. In other embodiments, the unsaturation ofblock B is reduced upon hydrogenation to less than 5% of its originalvalue, and the average unsaturation of the hydrogenated block polymer isreduced to less than 20% of its original value.

The block polymers of the vinyl aromatic monomer and the conjugateddiene may also be grafted with one or more of the above describedunsaturated monocarboxylic or dicarboxylic reagents. The carboxylicreagents include carboxylic acids per se and their functionalderivatives such as anhydrides, imides, metal salts, esters, etc., whichare capable of being grafted onto the selectively hydrogenated blockpolymer. The grafted polymer will usually contain from about 0.2 toabout 20%, and preferably from about 0.1 to about 10% by weight based onthe total weight of the block polymer and the carboxylic reagent of thegrafted carboxylic acid.

In order to promote the grafting of the carboxylic acid reagent to thehydrogenated block polymer, free radical initiators are utilized, andthese initiators usually are either peroxides or various organic azocompounds. The amount of initiator utilized generally is from about0.01% to about 5% by weight based on the combined weight of the combinedpolymer and the carboxylic reagent. The amount of carboxylic acidreagent grafted onto the block polymers can be measured by determiningthe total acid number of the product. The grafting reaction can becarried out by melt or solution mixing of the block polymer and thecarboxylic acid reagent in the presence of the free radical initiator.

The preparation of various selectively hydrogenated block polymers ofconjugated dienes and vinyl aromatic toohomers which have been graftedwith a carboxylic acid reagent is described in a number of patentsincluding U.S. Pat. Nos. 4,578,429; 4,657,970; and 4,795,782, and thedisclosures of these patents relating to grafted selectivelyhydrogenated block polymers of conjugated dienes and vinyl aromaticcompounds, and the preparation of such compounds are hereby incorporatedby reference. U.S. Pat. No. 4,795,782 describes and gives examples ofthe preparation of the grafted block polymers by the solution processand the melt process. U.S. Pat. No. 4,578,429 contains an example ofgrafting of Kraton G1652 (SEBS) polymer with maleic anhydride with2,5-dimethyl-2,5-di(t-butylperoxy) hexane by a melt reaction in a twinscrew extruder. (See Col. 8, lines 40-61.)

Examples of commercially available maleated selectively hydrogenatedpolymers of styrene and butadiene include Kraton FG1901X from Shell,often referred to as a maleated selectively hydrogenated SEBS polymer.

Block Polymers (Aiii)

The multilayered structure also includes a block polymer of a vinylaromatic monomer and a conjugated diene, or a partially hydrogenatedderivative thereof, or a selectively hydrogenated derivative thereof towhich has been grafted a unsaturated carboxylic reagent. (Aiii) isgenerally present in an amount from about 5%, or about 8% up to about20%, or to about 15% by weight. (Aiii) contains greater than 60% byweight bound vinyl aromatic monomer. In another embodiment, (Aiii) hasgreater than about 65%, or greater than about 70%, or greater than about72% by weight bound vinyl aromatic monomer. The vinyl aromatic monomerand the conjugated diene are described above. (See Block Polymer (Aii)).

Examples of useful block polymers having greater than 60% by weightbound vinyl aromatic monomer include Phillips K Resins 03, 04 and 05,available from Phillips Petroleum Company. Generally, the K-Resins havea high polystyrene content such as about 75%, and these resins aretransparent and rigid. One particularly preferred block polymer isK-Resin KR03 from Phillips. A similar material (75% styrene:25%butadiene) is available from Fina under the designation "Finaclear 520".

Core Layer (B)

The multilayer structure also contains a core layer. This core layer maybe prepared from one of three polymer compositions or polyolefinsdescribed herein, including polypropylene. The core layers are attachedto the cap layer by means know to those in the art. In one embodimentthe layer are attached without a glue, or tie, layer between the caplayer and the core layer.

Polymer Composition (B1)

The first polymer composition (B1) useful in preparing the core layer isa polymer composition comprising (i) from about 50% to about 80% byweight of at least one polyolefin, (ii) from about 10% to about 30% byweight of a polymer of a vinyl aromatic compound and an unsaturateddicarboxylic acid anhydride or imide, or mixtures thereof; and (iii)from about 5% to about 20% by weight of a block polymer of a vinylaromatic compound and a conjugated diene, a partially hydrogenatedderivative thereof, or a selectively hydrogenated derivative thereof towhich has been grafted a unsaturated carboxylic reagent.

Polyolefins (B 1i)

The polyolefins employed in the blends of the present inventiongenerally are semi-crystalline or crystallizable olefin polymersincluding homopolymers, copolymers, terpolymers, or mixtures thereof,etc., containing one or more monomeric units. The polyolefins (B1i) isgenerally present in an amount from about 50%, or about 55%, or about60% up to about 80%, or to about 75%, or to about 72% by weight.

Polymers of alpha-olefins or 1-olefins are preferred in the presentinvention, and these alpha-olefins may contain from 2 to about 20 carbonatoms. Alpha-olefins containing 2 to about 6 carbon atoms are preferred.Thus, the olefin polymers may be derived from olefins such as ethylene,propylene, 1 -butene, 1 -pentene, 4-methyl- 1 -pentene, 1 -octene, 1-decene, 4-ethyl-l-hexene, etc. Examples of polyolefins includepolypropylene, polyethylene, and ethylene propylene copolymers.

In one embodiment, the polyolefins include polypropylene andethylene-propylene polymers. (B1i) is generally present in an amountfrom about 50%, or about 55%, or about 60% up to about 80%, or to about75%, or to about 72% by weight. Propylene polymers may besemi-crystalline or crystalline in structure. The number averagemolecular weight of the propylene polymers is preferably above about10,000 and more preferably above about 50,000. In addition, it ispreferred in one embodiment that the apparent crystalline melting pointbe above about 75° C. and preferably between about 75° C. and about 250°C.. The propylene polymers useful in preparing the polymer blends of thepresent invention are well-known to those skilled in the art and manyare available commercially. Polypropylene are preferred propylenepolymers, and polypropylenes such as Aristech F007S, Aristech F007F(homopolymers), and Shell's 7C06 or Exxon's PD7132 or Aristech's 4007Fand 4040F (polypropylene-ethylene copolymers) are particularlypreferred.

The propylene polymers include at least one copolymer of propylene andethylene. The propylene ethylene copolymer will generally contain fromabout 1%, or about 4% to about 10%, or about 7% by weight of ethylene.In one embodiment, the ethylene content is about 6% by weight. In oneembodiment, the propylene ethylene copolymer is a random copolymer.

Processes useful in preparing the propylene ethylene copolymers usefulin preparing the present invention are well-known to those skilled inthe art and many such copolymers are available commercially. Such randomcopolymers may be prepared by any of a number of methods known in theart including those set forth in the Encyclopedia of Polymer Science &Engineering, Vol. 13, 2nd edition, Wiley & Sons, pp. 500-el seq. (andfootnotes cited therein), which is fully incorporated by referenceherein. Propylene ethylene copolymers useful in the present inventionare available commercially. Examples of these copolymers include FinaY-8573 and Z-7650 available from Fina Oil and Chemical Company, Dallas,Texas, U.S.A and Soltex 4208 available from Soltex Polymer Corporation,Houston, Texas, U.S.A.

Vinyl Aromatic Monomer/Carboxylic Reagent Copolymers (B1ii)

The polymer composition (B 1 ) also includes a polymer of a vinylaromatic monomer and an unsaturated carboxylic reagent (B1ii). (B1ii) istypically present in an amount from about 10S, or about 15% up to about30%, or to about 25% by weight of the polymer composition. The vinylaromatic monomers and unsaturated carboxylic reagents are describedabove. (See Polymers (Ai) and (Aii)). Preferably, the unsaturatedcarboxylic reagent is a maleic reagent, such as maleic acid, imide, oranhydride.

Block Polymers (B 1 iii)

The polymer composition (B 1 ) includes a block polymer of a vinylaromatic monomer and a conjugated diene, or a partially hydrogenatedderivative thereof, or a selectively hydrogenated derivative thereof towhich has been grafted a unsaturated carboxylic reagent. (B 1 iii) isgenerally present in an amount from about 5%, or about 8% up to about20%, or to about 15% by weight. The vinyl aromatic monomers and theconjugated dienes are described above. (See Polymers (Ai) and (Aii)). Inone embodiment, the block polymer is a multiblock polymer. Aparticularly useful multiblock polymer is Stereon 84 1, availablecommercially from The Firestone Tire & Rubber Company.

Polymer Composition (B2)

The core layer may also be formed from a polymer composition comprising(i) from about 50% to about 80% by weight of a polyolefin, (ii) fromabout 10% to about 30% by weight of a homopolymer of a vinyl aromaticmonomer, or a polymer of a vinyl aromatic toohomer and at least onetoohomer selected from the group consisting of acrylic acid or ester,methacrylic acid or ester, acrylonitrile and maleic anhydride; (iii)from about 5% to about 20% by weight of at least one block polymer of avinyl aromatic monomer and an aliphatic conjugated diene, a partiallyhydrogenated derivative thereof, or a selectively hydrogenatedderivative thereof to which has been grafted a unsaturated carboxylicreagent. The polyolefin (B2i), polymer of a vinyl aromatic monomer(B2ii) and the block polymer (B2iii) are described above. (B2i) isgenerally present in an amount from about 50%, or about 55%, or about60% up to about 80%, or to about 75%, or to about 72% by weight. (B1 ii)is typically present in an amount from about 10%, or about 15% up toabout 30%, or to about 25% by weight of the polymer composition. (B 1iii) is generally present in an amount from about 5%, or about 8% up toabout 20%, or to about 15% by weight.

Polymer Composition (B3)

The core layer of the multilayer structure may also be prepared from apolymer composition comprising (i) from about 70% by weight of at leastone polyolefin, (ii) from about 5% to about 30% by weight of a blockpolymer of a vinyl aromatic compound and a conjugated diene, a partiallyhydrogenated derivative thereof, or a selectively hydrogenatedderivative thereof to which has been grafted a unsaturated carboxylicreagent, wherein the block polymer is derived from at least about 60% byweight bound vinyl aromatic monomer; and (iii) from about 0.3% to about15% by weight of a block polymer of a vinyl aromatic compound and aconjugated diene, a partially hydrogenated derivative thereof, or aselectively hydrogenated derivative thereof to which has been grafted aunsaturated carboxylic reagent, wherein the polymer contains up to about50% by weight bound vinyl aromatic monomer.

The inventors have discovered that the combination of the block polymerswith different levels of aromatic content provides improved propertiesin combination, especially with the polyolefins. The polyolefins (B3i)and the block polymer (B3iii) are described above. (See Polyolefin (B1i)and Block Polymer (Aii), respectively). The low aromatic content blockpolymers are described above (see (Aii)). The high aromatic contentblock polymers are described above (see (Aiii)). Generally, (B3i) ispresent in an amount from about 70%, or about 75%, or about 80% up toabout 95%, or to about 90%, or to about 88% by weight. (B3ii) istypically present in an amount from about 5%, or from about 10% up toabout 30%, or to about 25%, or to about 20% by weight. (B3iii) istypically present in an amount from about 0.3%, or from about 0.5% up toabout 15%, or about 10% by weight. In one embodiment, (B3iii) is presentin an amount from about 0.3%, or about 0.5% up to 2%, or to about 1.5%,or to about 1% by weight.

The high aromatic content block polymer include high styrene contentblock polymers, such as Stereon 900 available from The Firestone Tire &Rubber Company. The polymer is believed to be derived from about 70% toabout 80% by weight styrerie.

Fillers (C)

The above polymer layers may contain one or more fillers of the typeused in the polymer art. Examples of fillers employed in a typicalcompounded polymer blend according to the present invention includetalc, calcium carbonate, mica, wollastonite, dolomite, glass fibers,boron fibers, carbon fibers, carbon blacks, pigments such as titaniumdioxide, or mixtures thereof. Preferred fillers are a commerciallyavailable talc such as R.T. Vanderbilt's Select-A-Sorb, Jet Fil andglass fibers. The amount of filler included in the blended polymers mayvary from about 1% to about 70% of the combined weight of polymer andfiller. Generally amounts from about 5% to about 45%, from about 30% toabout 40%, are included.

The fillers may be treated with coupling agents to improve the bondbetween the fillers to the resin. For example, the fillers can betreated with materials such as fatty acids (e.g., stearic acid),silanes, maleated polypropylene, etc. The amount of coupling agent usedis an amount effective to improve the bond between the fillers with theresin.

Preparation of Polymer Blends

The blended polymer compositions of the present invention can beprepared by techniques well known to those skilled in the art. Forexample, a particularly useful procedure is to intimately mix thepolymers using conventional melt mixing equipment such as a mill, aBanbury, a Brabcndcr, a single or twin screw extruder, continuousmixers, kneaders, etc. For example, the polymers may be intimately mixedin the form of granules and/or powder in a high shear mixer. Onepreferred process for preparing the blended polymers utilizes theFarrell Compact Processor, CP-23 and CP-57. Short residence times andhigh shear are readily obtained in a CP-23 and a CP-57. "Intimate"mixing means that the mixture is prepared with sufficient mechanicalshear and thermal energy to produce a dispersed phase which is finelydivided and homogeneously dispersed in the continuous or principalphase.

The layers such as the cap and core layers be applied by co-extrusion,laminating, etc., or the second layer can be applied from a solution ora dispersion of the cap in water or an organic liquid such as acetone.On drying, a film or cap layer is left on the layer comprising thecomposition of the invention. In another embodiment, multilayeredstructures can be prepared by co-extrusion.

Thermoformed articles having desired shapes can be produced from each ofthe blended polymer compositions of the present invention by

(A) feeding a sheet of the blended polymer composition of the inventionto a heating station;

(B) heating the sheet to its softening point; and

(C) feeding the softened sheet to a forming station where it isthermoformed into articles of the desired shape.

The present invention also includes polymer compositions. Morespecifically, the invention includes a polymer composition comprising(i) at least about 55% by weight of a homopolymer of a vinyl aromaticmonomer, or a polymer of a vinyl aromatic monomer and at least onemonomer selected from the group consisting of a mono- or dicarboxylicreagent and other vinyl monomers, (ii) from about 1% to about 45% byweight of at least one block polymer of a vinyl aromatic monomer and analiphatic conjugated diene, a selectively hydrogenated derivativethereof, or a selectively hydrogenated derivative thereof to which hasbeen grafted a unsaturated carboxylic reagent, wherein the block polymercontains up to about 50% by weight bound styrene, and (iii) from about0.3% to about 45% by weight of at least one block polymer of a vinylaromatic monomer and a conjugated diene, a partially hydrogenatedderivative thereof, or a selectively hydrogenated derivative thereof towhich has been grafted a unsaturated carboxylic reagent, wherein theblock polymer contains greater than about 60% by weight bound vinylaromatic monomer. The polymer composition is used in making the caplayer and is described above. The invention also includes polymercomposition comprising (i) from about 70% by weight of at least onepolyolefin, (ii) from about 5% to about 30% by weight of a block polymerof a vinyl aromatic compound and a conjugated diene, a partiallyhydrogenated derivative thereof, or a selectively hydrogenatedderivative thereof to which has been grafted a unsaturated carboxylicreagent, wherein the block polymer is derived from at least about 60% byweight bound vinyl aromatic monomer; and (iii) from about 0.3% to about15% by weight of a block polymer of a vinyl aromatic compound and aconjugated diene, a partially hydrogenated derivative thereof, or aselectively hydrogenated derivative thereof to which has been grafted aunsaturated carboxylic reagent, wherein the polymer is derived from upto about 50% by weight bound vinyl aromatic monomer. The polymercomposition is described above as (B3) and is used in making the corelayer.

Various features and aspects of the present invention are illustratedfurther in the examples that follow. While these examples are presentedto show one skilled in the art how to operate within the scope of thisinvention, they are not to serve as a limitation on the scope of theinvention where such scope is only defined in the claims. Moreover, inthe following examples, preparation of blends, compounds, injectionmolded specimens, mono layer or laminated sheets are illustrated. Theseexamples serve merely as illustrative embodiments of the presentinvention and are not to be considered limiting.

Unless otherwise indicated in the following examples and elsewhere inthe specification and claims, all parts and percentages are by weight,temperatures are in degrees centigrade and pressures are at or nearatmospheric.

EXAMPLES 1-15

Examples 1-6 are blended polymer compositions in accordance with thepresent invention which are prepared on a Farrell Compact Processor,CP-57 at a mixer rotor speed of 500 rpm and extruded at about 220° C.into strands which are passed through a water bath and air wipe prior topelletizing. Examples 7-8 are prepared on a Farrell Compact Processor,CP-12, at a mixer rotor speed of 700 rpm and extruded at 216°-220° C.into strands which are passed through a water bath and air wipe prior topelletizing. Examples 1-8 relate to polymer compositions useful inpreparing the cap layer of the multilayer structure. Examples 9-15relate to polymer compositions useful as core layers.

    ______________________________________                                                1   2      3     4    5    6     7    8                               ______________________________________                                        Dart 108 (PS)                                                                           60    60     60  65   65   70    --   --                            Mobil 7863                                                                              --    --     --  --   --   --    69.6 69.6                          (HIPS)                                                                        Stereon 841                                                                             10    --     --  --   --   --    --   --                            (43% styrene)                                                                 Kraton G1652                                                                            --    --     --  --   --   --    18.7 --                            (Maleated                                                                     SEBS)                                                                         Kraton    --    10     --  21.9 17.5 18.7  --   18.7                          FG1901X                                                                       (Maleated                                                                     SEBS)                                                                         Kraton    10    --      5  --   --   --    --   --                            G1701x                                                                        Phillips KR                                                                             20    --     20  13.1 --   11.3  11.3 11.3                          03 (75%                                                                       Styrene)                                                                      Stereon 900                                                                             --    15     15  --   --   --    --   --                            (73.5%                                                                        Styrene)                                                                      Stereon 881                                                                             --    15     --  --   17.5 --    --   --                            (78%                                                                          Styrene)                                                                      Irganox B225                                                                            --    --     --  --   --   --    0.4  0.4                           ______________________________________                                    

The following table contains polymer compositions which are useful inpreparing the core layer of the multilayer structure.

    ______________________________________                                                  9    10     11     12   13   14   15                                ______________________________________                                        Aristech TI-4007                                                                          67.7   38.86  67.7 38.86                                                                              --   --   38.16                           (PP)                                                                          Aristech F007S                                                                            --     --     --   --   84.2 55.7 --                              (PP)                                                                          Dart 108 (PS)                                                                             --     --     21.5 12.36                                                                              --   --   12.36                           Arco Dylark 250                                                                           21.5   12.36  --   --   --   --   --                              (SMA)                                                                         Stereon 841 (SB                                                                           10.8   6.18   --   --   0.7  0.5  --                              Block)                                                                        Stereon 900 (SB                                                                           --     --     --   --   15.1 10   --                              Block)                                                                        Kraton FG1901X                                                                            --     --     --   --   --   --   --                              (Maleated SEBS)                                                               Phillips KR 03 (SB                                                                        --     --     --   --   --   --   --                              Block)                                                                        Finaprene 414 (SB                                                                         --     --     10.8 6.18 --   --   6.18                            Block)                                                                        ECC Supercoat                                                                             --     40     --   40   --   --   41.49                           (CaCO.sub.3)                                                                  Polar 9110 (Talc)                                                                         --     --     --   --   --   31   --                              TiO.sub.2   --     2.5    --   2.5  --   --   1.0                             Lubricant   --     --     --   --   --   0.7  --                              Stabilizer  --     0.1    --   0.1  --   0.1  0.8                             Ultramarine Blue                                                                          --     --     --   --   --   --   0.01                            ______________________________________                                    

EXAMPLE 16

A multilayer structure is made by co-extruding polymer compositionsExamples 6 and 14 above, The polymer composition of Example 14 is placedin an extruder and heated to a melt temperature 220° C., The extruder isoperating at 100 RPM and has a head pressure of 2000 psi, Thecomposition of Example 14 is prepared in a co-extruder, The co-extruderis operating at 125 RPM and has a head pressure of 1750 psi, The polymercompositions from both extruders are extruded to a co-extrusion feedbackwhere the layers are brought together and then made to flow through asheet die at 205° C.. The co-extruded sheet then passes between a seriesof polish rolls which both cool and impart a surface to the sheet. Thepolymers form a multilayer sheet.

EXAMPLE 17

The multilayer structure from Example 16 is placed in a standard vacuumforming equipment. The sheet is heated to 177° C. until the sheet sagsabout 6 to 13 mm. The mold is closed to form a thermoformable article.

EXAMPLE 18

An extruded sheet prepared as in Example 16 with the composition ofExample 5 is heat laminated with an extruded sheet of the product ofExample 9 prepared by the procedure of Example 16 and subsequentlythermoformed into cups in a single operation.

EXAMPLE 19

A two-layer laminate is prepared in the following manner. A 40 railsheet of the composition of Example 2 is prepared by extrusion. To thissheet is heat laminated a 12 rail cap layer of Example 6.

EXAMPLE 20

A multilayer structure is prepared as described in Example 16 from thepolymer compositions of Examples 7 and 15 above. The polymercompositions are co-extruded through a sheet die to form a multilayerstructure.

EXAMPLE 21

A multilayer structure from Example 20 is placed in a standard vacuumforming equipment. The sheet is heated to 177° C. until the sheet sagsabout 6 to 13min. The mold is closed to form a thermoformable article.

While the invention has been explained in relation to its preferredembodiments, it is to be understood that various modifications thereofwill become apparent to those skilled in the art upon reading thespecification. Therefore, it is to be understood that the inventiondisclosed herein is intended to cover such modifications as fall withinthe scope of the appended claims.

We claim:
 1. A multilayer thermoformable structure comprising(A) atleast one cap layer of a polymer composition comprising (i) at leastabout 50% to about 80% by weight of a high impact polystyrene, (ii) fromabout 0% to about 45% by weight of at least one block polymer of a vinylaromatic monomer and an aliphatic conjugated diene, a selectivelyhydrogenated derivative thereof, or a selectively hydrogenatedderivative thereof to which has been grafted a unsaturated carboxylicreagent, wherein the block polymer contains up to about 50% by weightbound styrene, and (iii) from about 0% to about 45% by weight of atleast one block polymer of a vinyl aromatic monomer and a conjugateddiene, a partially hydrogenated derivative thereof, or a selectivelyhydrogenated derivative thereof to which has been grafted a unsaturatedcarboxylic reagent, wherein the block polymer contains greater thanabout 60% by weight bound vinyl aromatic monomer, with the proviso thatthe cap layer includes at least one of (Aii) or (Aiii); and (B) at leastone core layer selected from the group consisting of(1) at least onepolymer composition comprising (i) from about 50% to about 80% by weightof at least one polyolefin, (ii) from about 10% to about 30% by weightof a polymer of a vinyl aromatic compound and an unsaturateddicarboxylic acid anhydride or imide, or mixtures thereof; and (iii)from about 5% to about 20% by weight of a block polymer of a vinylaromatic compound and a conjugated diene, a partially hydrogenatedderivative thereof, or a selectively hydrogenated derivative thereof towhich has been grafted a unsaturated carboxylic reagent; (2) at leastone polymer composition comprising (i) from about 50% to about 80% byweight of a polyolefin, (ii) from about 10% to about 30% by weight of ahomopolymer of a vinyl aromatic monomer, or a polymer of a vinylaromatic monomer and at least one monomer selected from the groupconsisting of acrylic acid or ester, methacrylic acid or ester,acrylonitrile and maleic anhydride; (iii) from about 5% to about 20% byweight of at least one block polymer of a vinyl aromatic monomer and analiphatic conjugated diene, a partially hydrogenated derivative thereof,or a selectively hydrogenated derivative thereof to which has beengrafted a unsaturated carboxylic reagent; (3) at least one polymercomposition comprising (i) from about 70% by weight of at least onepolyolefin, (ii) from about 5% to about 30% by weight of a block polymerof a vinyl aromatic compound and a conjugated diene, a partiallyhydrogenated derivative thereof, or a selectively hydrogenatedderivative thereof to which has been grafted a unsaturated carboxylicreagent, wherein the block polymer is derived from at least about 60% byweight bound vinyl aromatic monomer; and (iii) from about 0.3% to about15% by weight of a block polymer of a vinyl aromatic compound and aconjugated diene, a partially hydrogenated derivative thereof, or aselectively hydrogenated derivative thereof to which has been graded aunsaturated carboxylic reagent, wherein the polymer is derived from upto about 50% by weight bound vinyl aromatic monomer.
 2. The structure ofclaim 1 wherein the vinyl aromatic monomer is styrerie and theconjugated diene is independently selected from the group consisting ofbutadiene and isoprene.
 3. The structure of claim 1 wherein the caplayer (A) comprises a polymer composition comprising (i) from about 50%to about 80% by weight of high impact polystyrene, (ii) from about 10%to about 30% by weight of a selectively hydrogenated block polymer ofstyrene and isoprene or butadiene to which has been grafted maleic acidor anhydride, and (iii) from about 5% to about 15% by weight of a blockpolymer of styrerie and isoprene or butadiene, or a partiallyhydrogenated derivative thereof.
 4. The structure of claim 1 wherein thecore layer (B) comprises the polymer composition (1), wherein (i) ispolypropylene, (ii) is a polymer of styrene and maleic acid orarthydride, and (iii) is a block polymer of styrene and isoprene orbutadiene, or a partially hydrogenated derivative thereof.
 5. Thestructure of claim 1 wherein the core layer comprises the polymercomposition (B2), wherein (i) is polypropylene, (ii) is polystyrene, and(iii) is a block polymer of styrerie and isoprene or butadiene, or apartially hydrogenated derivative thereof.
 6. The structure of claim 1wherein the core layer comprises the polymer composition (B3), wherein(i) is polypropylene, and (ii) and (iii) are independently a blockcopolymer of styrerie and isoprene or butadiene, or a partiallyhydrogenated derivative thereof.
 7. The structure of claim 1 wherein thecore layer (B) further comprises (D) at least one filler.
 8. Amultilayer thermoformable structure comprising(A) at least one cap layerof a polymer composition comprising (i) at least about 50 % to about 80%by weight of a high impact polystyrene, (ii) from about 10% to about 30%by weight of at least one selectively hydrogenated block polymer of avinyl aromatic monomer and an aliphatic conjugated diene to which hasbeen grafted a unsaturated carboxylic reagent, and (iii) from about 5%to about 15% by weight of at least one block polymer of a vinyl aromaticmonomer and a conjugated diene or a partially hydrogenated derivativethereof; and (B) at least one core layer selected from the groupconsisting of(1) at least one polymer composition comprising (i) fromabout 50% to about 80% by weight of polypropylene or anethylene-propylene polymer, (ii) from about 10% to about 30% by weightof a polymer of a vinyl aromatic compound and an unsaturateddicarboxylic acid anhydride or imide, or mixtures thereof; and (iii)from about 5% to about 20% by weight of a block polymer of a vinylaromatic compound and a conjugated diene, or a partially hydrogenatedderivative thereof; (2) at least one polymer composition comprising (i)from about 50% to about 80% by weight of polypropylene or anethylene-propylene copolymer, (ii) from about 10% to about 30% by weightof a homopolymer of a vinyl aromatic monomer; (iii) from about 5% toabout 20% by weight of at least one block polymer of a vinyl aromaticmonomer and an aliphatic conjugated diene, or a partially hydrogenatedderivative thereof; (3) at least one polymer composition comprising (i)from about 70% by weight of polypropylene or an ethylene-propylenecopolymer; (ii) from about 5% to about 30% by weight of a high vinylaromatic content block polymer of a vinyl aromatic compound and aconjugated diene, or a partially hydrogenated derivative thereof,wherein the block polymer is derived from at least about 60% by weightbound vinyl aromatic monomer; and (iii) from about 0.3% to about 15% byweight of a block polymer of a vinyl aromatic compound and a conjugateddiene, or a partially hydrogenated derivative thereof, wherein thepolymer is derived from up to about 50% by weight bound vinyl aromaticmonomer.
 9. The structure of claim 8 wherein the vinyl aromatic monomerof (A) and (B) is styrene and the conjugated diene of (A) and (B) isindependently selected from the group consisting of butadiene andisoprene.
 10. The structure of claim 8 wherein the cap layer (A)comprises a polymer composition comprising (i) from about 50% to about80% by weight of high impact polystyrene, (ii) from about 10% to about30% by weight of a selectively hydrogenated block polymer of styrene andisoprene or butadiene to which has been grafted maleic acid oranhydride, and (iii) from about 5% to about 15% by weight of a blockpolymer of styrene and isoprene or butadiene, or a partiallyhydrogenated derivative thereof.
 11. The structure of claim 8 whereinthe core layer (B) comprises the polymer composition (1), wherein (i) ispolypropylene, (ii) is a polymer of styrene and maleic acid oranhydride, and (iii) is a block polymer of styrene and isoprene orbutadiene, or a partially hydrogenated derivative thereof.
 12. Thestructure of claim 8 wherein the core layer comprises the polymercomposition (B2), wherein (i) is polypropylene, (ii) is polystyrene, and(iii) is a block polymer of styrene and isoprene or butadiene, or apartially hydrogenated derivative thereof.
 13. The structure of claim 8wherein the core layer comprises the polymer composition (B3), wherein(i) is polypropylene, and (ii) and (iii) are independently a blockcopolymer of styrene and isoprene or butadiene, or a partiallyhydrogenated derivative thereof.
 14. The structure of claim 8 whereinthe core layer (B) further comprises (D) at least one filler.
 15. Thestructure of claim 14 wherein the filler is talc, calcium carbonate, ora glass fiber.